This invention relates to head positioning servo systems for reducing misalignment between a read or write head and a data track and also to servo transducers for use with head positioning systems.
Head positioning servo systems are employed in many contexts requiring accurate positioning of a read or write head over a selected data track. Miss-registration between the head and the data track can cause data errors during readback and catastrophic data loss on adjacent tracks during writing.
In multitrack magnetic tape storage systems, random lateral tape motion ("LTM") is a limiting factor in achieving higher track densities and thus higher user data capacity per tape. LTM is an undesirable motion of the tape in the lateral direction, that is transverse to the tape transport direction. LTM may be caused by many factors including, tape slitting variations, tension variations, imperfections in the guiding mechanism, friction variations mainly at the head, and environmental factors such as heat and humidity. These factors affect LTM in various ways. Some may cause abrupt momentary jumps while others may cause a static shift. Generally, LTM is unpredictable and unrepeatable.
Various techniques for increasing the track density on magnetic tape employ recording servo information on the tape to provide positioning information. Some systems record a continuous track of servo information which is then used as a position reference signal. Other systems intersperse or embed the servo information with user data. Yet another system, described in U.S. Pat. No. 5,452,152, uses two auxiliary servo heads to follow each edge of an adjacent track for head positioning.